Rotary kilns are employed to pyro-process materials such as lime, cement, clinker, alumina, and other calcined or burned products. Conventional rotary kilns include a refractory lining of brick or monolithic casting. The refractory lining protects the outer shell against deterioration due to the extreme temperatures at which pyro-processing occurs, while concurrently mitigating heat loss through the outer metallic shell of the rotary kiln. Artisans have long constructed refractory linings for rotary kilns comprised of refractory bricks or blocks of uniform shape by successively laying these shapes according to methods well known. The VDZ and ISO schedules teach the shapes known in the art for rotary kiln applications, which include wedges, arches, keys and other designs.
Conventional rotary kilns may also include a lifter section, arranged parallel to the length of the kiln, which agitates the material passing through the kiln. Lifters cause this desirable agitation by capturing a portion of the material upon rotation of the kiln, carrying it upwards along the wall of the kiln before releasing it as the lifter rotates towards the uppermost point of rotation. As the material falls off the lifter and towards the lowest point of rotation, it passes through the hot gases existing in the kiln. Thus, as a consequence of increasing agitation, the lifter section enhances the heat transfer from the rotary kiln to the material so processed.
Prior art designs of rotary kilns linings have included lifter sections comprising a single brick attached to the inner shell by way of metal rods and installed for a certain portion of the length of the overall kiln. More recent designs include lifter sections formed of monolithic castings of refractory material. These inflexible prior art designs require specific set-up procedures to ensure the survivability of the base material which, in general, limit the application to the cooler regions of the rotary kiln where the effectiveness as a heat transfer system is minimized. Put another way, prior art designs have generally excluded lifter sections from the hottest portion of the kiln, known as the burning zone, because the extreme temperature and compressive forces of the processed material adversely affect the integrity of the structure. This exclusion, however, causes wasteful heat loss as it prevents sufficient agitation as the material traverses this portion of the rotary kiln. Also, because the burning zone is typically located at or towards the discharge end of the rotary kiln, the material may exit these prior art kilns with less than a sufficient degree of mixing.